The long-term objectives of this study are to define the structural principles utilized by the "immunoglobulin-like" alpha/beta T cell receptor molecule (TCR) in the recognition of its ligand, i.e. the antigen in association with the polymorphic major histocompatibility complex encoded (MHC) molecule. This unique ligand recognition property of the TCR is the basis for selection of individual cells from the total available in the repertoire. Defining the structural features of the TCR which relate to the recognition of its ligand is a pre-requisite for the design of experimental strategies aimed at modulating antigen-specific T cell responses and understanding the basis of MHC-linked immune disorder in humans. The gene transfer approach with the alpha and the beta TCR genes will be used to carry out this analysis in a simple model system established in this laboratory. This model system permits systematic changes to be made in each of the three interacting components, the antigen, the MHC molecule and the TCR. A large panel of T cell clones has been generated with well characterized specificities for synthetic tide antigens (within aa 74-96 of hen lysozyme) and several MHC molecules (Ak, Ek, Ab, and Abm-12). The analysis has been further simplified by a careful selection of sets of T cell clones from this panel which can be used to carry out reciprocal experiments. These sets of T cells possess (a) closely related but yet distinct antigen and/or MHC ligand specificities, and (b) TCRs with identical or very similar segments in the alpha and/or the beta chains. These TCR genes will be used to probe the specific structural features of the alpha and the beta chains by relating them to predictable changes in the functional reactivity of the TCRs expressed in transfectant cells. To overcome the inherent ambiguities present in the execution and interpretation of previous experiments, a novel approach will be used to develop mutant recipient cell lines which do not express either the endogenous alpha or the beta chains. In addition, the relationship between the TCR specificity for the antigen/MHC ligand and the MIs antigens will be determined with transfectants expressing both reactivity.